The present invention generally relates to a communication system. More particularly, this invention is concerned with a multi-medium communication system in which a plurality of different type terminal equipments or units are connected to a single transmission path and which system is employed for transmission of a plurality of various types of information such as computer data, video signal, audio signal and others over a single transmission path.
The communication system using a transmission line or path is globally classified into a base band communication system in which a pulse signal corresponding to a sequence of digital codes "1" and "0" is transmitted over a transmission path on one hand and a broad band communication in which a frequency band on the transmission path is divided into a plurality of frequency ranges (channels), wherein a single transmission path is shared in use for transmission of a plurality of modulated signals (analog signals) having respective center frequencies corresponding to the individual channels. The broad band communication system is suited for the multi-medium communication for transmitting concurrently different types of information such as audio and video information by virtue of the capability of establishing a plurality of logic channels on a single transmission path.
As one of the utilization mode of the broad band communication system, there has been reported a communication system in which information of a base band network is accommodated in one of channels of a broad band network. In this connection, reference may be made to A. Sabato et al's paper entitled "A System of Broad Band Network and its Applications" presented on a study meeting held by The Institute of Electrical Engineers of Japan (Document Data No. IP-83-3). According to this proposal, the digital signal of the base band is once modulated to an analog signal having a predetermined carrier frequency through frequency modulation or phase modulation and thereafter sent out onto a transmission path of the broad band network. This known system is however disadvantageous in that all the terminal units or devices handling the base band signal require respective high frequency modems for modulation/demodulation of the digital signal to/from the broad band signal (analogue signal) and involve necessarily complicated structure of the terminal unit. Beside, the known system can not always be applied to all the existing base band systems.